Large model viaducts (steel)

[Torr Giffard LSWR 1951-71]

Aft'noon all,

 

I'm in the process of designing a shortened version of the Tavy viaduct for Tor Giffard. The prototype is still a working viaduct and even with access arranged views of the structure below the rail deck are difficult to obtain. The similar bowstring, steel viaduct at Little Petherick creek on the former Padstow route is however completely accessible and good views of the essential below deck metalwork structure are much easier to obtain. Obviously, the Tavy viaduct was used for many years as a twin track main line viaduct whereas the one at Little Petherick was on a single track branch. These are a few views of the latter viaduct

 

   

 

On the Tavy version there appears to be 4 longitudinals within each bowstring arch with stretchers at regular intervals tieing them together, along with wider spaced, bigger diameter (8ft prototype) caissons.  

 

 

The above picture (from a currently unknown photographer) clearly shows a fundamental difference between the two viaducts in terms of the structural steelwork...it is integral to the bowstring arch structure on the Tavy but beneath the deck on the Petherick...giving the Tavy viaduct a much cleaner, streamlined profile. The top of the railway line can be seen running above the top of the outer bowstring sideframe member. 

 

 

This view from a currently unknown photographer illustrates 4 likely main longitudinals within each bowstring section with regular stretchers (9 equi. spaced)

 

A few comparative measurements of the depth of the bowstring side frame on the above picture, relative to the known gap between the rails suggests that 7mm would be appropriate as the depth of the side frame on the model. 

 

Many thanks for any help

 

Dave

[jamie92208]

I'm currently building several bridges for Lancaster Green Ayre and have the original plans for the main viaduct over the Lune. That was an 8 span curved bridge (Still in existance)with steel plate side members whuch were straight. The Caissons, in a river with a high tide range were 6' diameter increasing to 10' at the river bed. There were no extra londitinals just T girders acrosss between the main side members with curved plsteew linking them forming what I believe were known as 'jack arches' From looking at your pictures it looks to be a simialar arrangement. However it does look as if there were some extra longditudinals but they appear to only run between each set of cross members.There were no readily available long H girders in those days and most things were built up from 1/2" plate T and L sections rivetted together The longditudinals on the sides o my bridge started with one thickness at the caissons then thickened to 7 plates thick in their centres. The Cross girdes would supply most of the strength necessary for supporting the track. I presume that this has ballasted track therefore the decking would have been steel plate which would work well on such a structure.

 

The ties between the caissons look to be identical to the ones that I've had to design. They would be made up of simple cahnnels. There are pictures on my layout thread of how they look. I've added one below.

 

 

All the best with the project.

 

 

Jamie

[Torr Giffard LSWR 1951-71]

Thanks Jamie...useful picture.

 

Cheers

 

Dave

[jamie92208]

Thanks Jamie...useful picture.

 

Cheers

 

Dave

If you need any more info PM me.

 

Jamie

[Peter Bedding]

I produced the attached cross section of Bridge 613 (aka Meldon Viaduct) for my research some years ago. A Forum search (Bridge 613) will lead to a posting that I made in the past.

 

 

Whilst the Tavy Viaduct is a much different beast, some of the cross sectional dimensions may be of use.

 

With pedant mode on, it might be worth noting that these 19th century structures used cast and wrought iron for the most part, which is why there is so much left.

 

Hth

 

PB

[Torr Giffard LSWR 1951-71]

Thank you Peter,

 

There can't be too much information.

 

Cheers

 

Dave